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In North Carolina, there have been only 10 reports of stranded hawksbill sea turtles since stranding records were kept beginning in the mid-1980s; all were small juveniles (≤25 cm straight carapace length), and all were observed between 2001 - 2009 (NCWRC Sea Turtle Stranding and Salvage Network, unpublished data). In contrast, stranded loggerhead, green, Kemp’s ridley and leatherback turtles are found annually in North Carolina (<https://seaturtle.org/strand>). Of sea turtle nests found on North Carolina beaches, the majority are laid by loggerheads, with occasional nests laid by green, leatherback and Kemp’s ridley turtles (Bowen et al. 1994; Woodson & Webster 1999; Rabon et al. 2003).

During the second half of the 2015 nesting season in North Carolina, two hawksbill nests were documented at Cape Hatteras National Seashore, which is located on southern Hatteras Island in Dare County, North Carolina (Table 1). Both nests were initially recorded as being laid by loggerhead turtles, based on characteristics of the crawl left on the beach by the nesting females, and both clutches were relocated because they were laid in a zone that is prone to daily overwash and erosion in the late summer and early fall. However, through genetic analysis, we were able to conclusively identify these two nests as hawksbill.

Table 1. Descriptive data of the two hawksbill sea turtle clutches laid in North Carolina in 2015.

Eggshell samples were collected as part of an ongoing loggerhead turtle genetic capture-recapture project aimed at identifying individual females nesting north of Florida for the estimation of population size, clutch frequency, remigration intervals, and annual survival (<https://seaturtle.org/nestdb/genetics>). Eggshell samples were processed in accordance with the standard eggshell DNA extraction and genotyping protocols as previously described (Shamblin et al. 2011). Briefly, a single fresh egg is collected from each nest. The egg is opened, its contents discarded, and the eggshell is preserved in 95% ethanol prior to DNA extraction. Extracted maternal genomic DNA is amplified at 16 microsatellite markers to produce a unique genetic tag for each nesting female. Of the markers currently used, there are five that can also identify hawksbill turtles: CcP1H11, CcP1G03, CcP5C08, CcP1F01, CcP2H12 (Shamblin et al. 2007; 2009; CJN and BMS unpublished data). For the eggshell samples collected from the two clutches in Table 1, all five of these markers indicated that the alleles were pure hawksbill. Also, egghshell samples from both nests in Table 1 had identical genetic fingerprints for the 13 loci available for comparisons, meaning that the same individual laid both clutches.

In order to assess possible nest beach origins for this female, mitochondrial DNA from both samples was analyzed as previously described, except using primer LCM rather than LTEi9 (Gorham et al. 2014). Briefly, an 817 base pair (bp) fragment of the mitochondrial control region was amplified using primers LCM and H950 and sequenced using LCM and an internal sequencing primer, Cc271. Comparisons with reference sequences from Genbank confirmed that this female carried haplotype EiA48. To date, this haplotype has not been found in any western Atlantic nesting populations, but it has been found in foraging populations. It was previously reported in two of 18 juveniles foraging around Ascension Island in the central Atlantic (Putman et al. 2014). An analogous haplotype, EiBR7 (739 bp EiBR7 is inclusive within the EiA48 sequence), was detected in 6% of juveniles foraging around the Rocas Atoll and the Fernando de Noronha Archipelago off the northeastern coast of Brazil (Vilaça et al. 2013). The 380 bp version of these haplotypes, EATL, is the dominant haplotype in eastern Atlantic foraging aggregations, accounting for 68% of Cape Verde juveniles and 92% of Príncipe juveniles (Monzón-Argüello et al. 2010; 2011). EATL been reported in only a single individual in the Northwest Atlantic, a juvenile foraging near Buck Island, United States Virgin Islands (Bowen et al. 2007). The only known nesting source in the Atlantic for EATL is the Príncipe Island rookery off the west coast of Africa (Monzón-Argüello et al. 2011), and some of these females were carrying EiA48 specifically (Monzón-Argüello pers. comm. 2016). EiA48 is also identical to the 766 bp EiIP-16 (haplotype EiIP-16 is inclusive within EiA48), and this haplotype has been recorded at low frequency in the Seychelles and Chagos Archipelago nesting populations that comprise the western/central Indian Ocean genetic stock (Vargas et al. 2016).

Trans-Atlantic dispersal of oceanic juveniles was previously invoked to explain the presence of neritic juvenile hawksbills carrying apparent Eastern Atlantic haplotypes on Western Atlantic foraging grounds (Bowen et al. 2007, Vilaça et al. 2013). This connectivity has been further substantiated by three tag returns for hawksbills tagged by Project TAMAR as juveniles in Brazil later appearing along the west coast of Africa (Vilaça et al. 2013). Storm-forced dispersal of oceanic juveniles has been implicated to explain the presence of juveniles outside of their normal distribution, and residence in these novel juvenile foraging areas may in turn affect adult migratory pathways for these wayward turtles (Monzón-Argüello et al. 2012). Adult female hawksbill turtles typically exhibit strong natal homing, so much so that rookeries on the leeward and windward coats of Barbados separated by less than 25 km are genetically distinct populations (Browne et al. 2009). Nonetheless, natal homing is not absolute, and female straying is important for colonization of novel nesting habitats. Given the sum of the evidence, it is plausible that the hawksbill female that nested in North Carolina, USA, originated from the nesting colony at Príncipe Island in the East Atlantic, representing a possible transoceanic colonization event by this species. However, not all hawksbill rookeries in the Atlantic have been genetically characterized, so the possibility of nesting relocation within the Western Atlantic cannot be ruled out.

Regardless of where the hawksbill female came from, these two nests are >800 km north of the nesting beaches in central Florida, which previously had been considered to be the northernmost nesting area for this species in the western Atlantic (Meylan & Redlow 2006). Globally, these two nests are the furthest north (>35° north of the equator) of any known hawksbill sea turtle nest (<http://seamap.env.duke.edu/swot>).

The two hawksbill nests in North Carolina were laid 53 days apart. The average inter-nesting interval for hawksbills is around 14 days (Kamel & Delcroix 2009), suggesting that this turtle may have laid up to three other clutches between the two nests documented on Cape Hatteras. However, extensive sampling of all documented sea turtle clutches laid in Georgia, South Carolina, North Carolina and Virginia during 2015 did not reveal any other hawksbill nests (CJN and BMS, unpublished data). Possible explanations for these missed nests include: the female migrated to and nested on some other beach that is outside of the ongoing DNA capture-recapture study; the turtle nested within the study area but the nesting crawls and eggs were not sampled due to wind/rain that obscured them; the turtle expelled her eggs at sea (Beyneto & Delcroix 2005), or she nested only twice that year, 53 days apart.

Initially, when the nesting crawls were found, they were categorized as being made by loggerheads. This is not surprising: both species have similar nesting crawls, and average egg diameter and average clutch size are similar for the two species (Hirth 1980; van Buskirk & Crowder 1994). On nesting beaches used by both loggerheads and hawksbills in the same season, species identification is usually done following incubation, when nest contents are inventoried and species-specific patterns of carapacial scutes can be discerned (Serafini et al. 2009). Although the nesting female who laid these two clutches was pure hawksbill, it is possible that she mated with a different species and produced hybrid offspring (Karl et al. 1995). In Bahia, Brazil, where both species nest, hybridization between hawksbill and loggerhead turtles is common: approximately 40% of morphological hawksbills carry loggerhead mitochondrial DNA (Lara-Ruiz et al. 2006). Analyses of Brazilian hybrid sea turtle nuclear DNA, which is inherited from both parents, confirm that these hybrids are fertile and capable of back crossing with both parental species (Vilaça et al. 2012). Unfortunately, no hatchling or embryo samples were collected from the hawksbill nests in North Carolina. Thus, it is unknown whether the hatchlings were pure hawksbill or possibly hawksbill x loggerhead hybrids.

The second clutch of hawksbill eggs was lost to severe erosion from a week-long northeastern storm with sustained 20-30 mph NE winds, and beach front wave heights ranging from 4-8 feet. This, in turn, kept park staff from employing further protective measures, and thus there was no chance to identify species by visual inspection of live or dead hatchlings/embryos. However, species identification was confirmed by analysis of maternal DNA found in fresh eggshell collected this nest. This exemplifies the power of this technique to identify maternal identity of clutches lost during incubation because of environmental impacts and also to document nesting events by rare species that might have otherwise been missed.

Acknowledgments. The NC Sea Turtle Project is supported by the NC Wildlife Resource Commission Nongame & Endangered Wildlife Fund, the US Fish & Wildlife Service, the National Park Service, Cape Hatteras National Seashore Resource Management staff, in addition to other federal, state, local, and private institutions and individuals. Funding for the genetic mark-recapture project came from a NOAA Fisheries Species Recovery Grant. The authors thank Kelly Stewart for insightful comments and suggestions.

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